In-situ production of oil from strata of low permeability



Juiy 22, 1969 H. w. PARKER 3,456,731

IN'SITU PRODUCTION OF OIL FROM STRATA OF LOW PERMEABILITY Filed May 18, 1967 AIR 24 v paoouceo FUEL. GAS 23 F PRODUCED FLUIDS mamas 215K smas'xa INVENTOR.

H. W. PARKER A 7' TO/PNE VS nited States Patent 3,456,731 IN-SITU PRODUCTION OF OIL FROM STRATA OF LOW PERMEABILITY Harry W. Parker, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Filed May 18, 1967, Ser. No. 639,493 Int. Cl. E21h 43/24 US. Cl. 166256 Claims ABSTRACT OF THE DISCLOSURE Oil is produced in situ from an oil-yielding stratum of low permeability, such as an oil shale or a tar sand, penetrated by an injection well and a production well by providing a pathway for gas thru a substratum adjacent the oil-yielding stratum, injecting air thru the injection well so as to produce it in the production well thru said pathway, admixing fuel with the injected air to form a combustible mixture in said production well, burning the resulting combustible mixture in the production well within the stratum to be produced so as to heat and produce oil therefrom, and recovering the produced oil from the production well. Fuel gas is injected either into the air flowing through the injection well or directly thru a burner in the production well adjacnet the bottom of the stratum being produced.

This invention relates to an improved process or method for producing heat in an oil shale or other oil-yielding stratum of low permeability so as to produce oil from the shale.

Oil shales and other oil-yielding strata of low permeability present special problems in developing in situ recovery processes by either inverse or direct drive. The extremely low permeability, which is zero in an oil shale and insuflicient in other strata of low permeability to permit air injection therethru at suflicient rates to support combustion, is the crux of the problem. Processes which rely on fractures thru the oil shale usually fail due to plastic flow of the oil shale from heating thereby closing the fracture and shutting off the flow of air. Blindi hole techniques, other than electric heating, require simultaneous flow of a hot fluid and a cold fluid adjacent each other in the well resulting in heat exchange between the two fluids which makes suflicient movement of heat to the oil shale diflicult. The present invention is concerned with a method of operation which overcomes both of these problems.

Accordingly, it is an object of the invention to provide an improved process or method for heating an oil shale or other oil-yielding stratum of low permeability so as to produce oil therefrom. Another object is to provide a method of producing oil from an oil shale or similar stratum which conserves heat. A further object is to provide an oil production method applicable to oil-yielding strata of low permeability, such as an oil shale or a tar sand, utilizing fractures which do not become plugged or sealed due to expansion of the stratum from heat. Other objects of the invention will become apparent to one skilleld in the art upon consideration of the accompanying disclosure.

A broad aspect of the invention as applied to an oilyielding stratum of low permeability penetrated by an injection well and a production well comprises providing a flow path for air between the wells thru the substratum adjacent the bottom of the oil-yielding stratum, injecting air thru the injection well so as to produce it in the production well thru the flow path provided, admixing fuel with the air to form a combustible mixture in the production well, burning the resulting combustible mixture in the production well within the oil-yielding stratum 3,456,731 Patented July 22, 1969 ICC so as to heat and produce oil therefrom, and recovering the oil thus produced from the production well. In one embodiment of the invention, a burner is disposed on the lower end of a tubing string in the production well extending to the bottom of the oil-yielding stratum and fuel is injected thru the tubing string and the burner to form a combustible mixture adjacent the burner by mixing with the air injected thru the passagewayunderneath the oil-yielding stratum. In another embodiment, fuel gas is injected with the air entering the injection well to provide a combustible mixture passing thru the passageway between wells.

Usually, it is necessary to fracture the substratum by conventional fracturing methods and introduce a propping agent to the resulting fracture to maintain a passageway between wells. However, in isolated instances there may be suflicient permeability in the substratum or natural fractures therein to render air passage between wells suflicient and feasible at reasonable injection pressures. In such situations, fracturing is not necessary to operation of the process.

The ascending hot combustion gas in the production well directly heats the face of the oil shale or other oilyielding stratum being produced and heat moves thru the shale laterally from the production well, penetrating deep within the shale and producing oil principally in vapor form from the oil shale. As the process continues, eventually the shale is heated all the way to the injection well so that oil in vapor form is produced into this well. To facilitate the operation, air injection thru the injection well is effected thru a tubing string running to the level of the bottom of the oil shale with a packer set at this level around the tubing string so that produced fluids may be recovered from the annulus of the injection well. When fuel gas is included in the injected air, it is desirable to stay below the explosive limit or mix the gas and air downhole. In the event excessive temperatures are created at the bottom of the production well, control can be effected by including an inert gas in the injected air.

Another variation in the process comprises shutting off the flow of fuel thru the burner downhole in the production well after a substantial burning period has elapsed so that coke is formed on the well walls, and burning coke thus formed with the injected air from the passageway between wells. Alternation of burning with injected fuel and burning the coke on the well wall is within the scope of the invention.

A more complete understanding of the invention may be obtained by reference to the accompanying schematic drawing which is an elevational view thru an oil shale penetrated by a production well and an injection well connected below the shale with a fracture for performing the invention.

Referring to the drawing, an oil shale 10 is penetrated by an injection well 12 and a production well 14, both extending into substratum 16. Oil shale deposits are usually exceedingly thick, it not being unusual for them to be several hundred feet in thickness. Such oil shale deposits are usually at shallow depth so that overburden 18 is relatively thin, oftentimes, less than one hundred feet in thickness and rarely over a thousand feet in thickness. Both wells are cased to the top of the shale. Injection well 12 is provided with a tubing string 20' extending to the bottom of the shale where it is packed ofi by packer 22. A fuel gas injection line 23 and an air injection line 24 connect with tubing string 20 at ground level. Line 26 connects with the annulus of well 12 at ground level for withdrawal of produced fluids from well 12. Packer 22 prevents mixing of produced fluids in well 12 with the injected air passing thru tubing string 20. Tubing string 28 in well 14 extends to the bottom of stratum 10 and is provided with burner or burners 30 on the lower end thereof. A fuel line 32 connects with the tubing string 28 at the Well head for supplying fuel in the form of a fuel gas to burner 30. Burner 30 is provided with an ignitor not shown, for igniting the combustible mixture resulting from the ascension of air upwardly thru well 14 introduced thereto from fracture or other passageway 34 in substratum 16. Line 36 connects with the annulus of well 14 at the well head and provides means for withdrawing produced fluids from this well, including vaporized shale oil, fuel gas produced by the heating, and inert gas including nitrogen and combustion gases.

Lines 38 represent the propagation of the heat front thru the oil shale from production Well 14 toward injection well 12. Eventually the heat front reaches the injection well and produced fluids enter the injection well as indicated by the arrows 40. Any liquid oil produced in either well is readily producible by pumping in conventional manner.

The maximum temperature in production well 14 occurs just above burner 30 and combustion conditions are ontrolled so that this temperature does not exceed about 1250 or 1300 F. The simplest method of controlling this maximum temperature comprises injecting an inert gas in admixture with the air injected into tubing string 20 from line 24.

In operating without burner 30 in well 14, sufiicient fuel gas is injected thru line 23 into the injected air stream from line 24 to provide a combustible but not explosive mixture which passes thru passageway 34 into the bottom of Well 14 and is ignited therein by a suitable ignitor such as a fuse, electric spark, or other suitable ignition means. There is little or no problem of flame propagation thru fracture 34 because of its limited thickness which results in gas flow rates greater than flame propagation rate. In the event that the porosity or permeability of substratum 16 is sufiicient to permit injection therethru without fracturing, flame propagation thru the substratum will not occur.

In order to illustrate the invention without unduly and unnecessarily restricting the scope thereof, the following specific example is presented.

EXAMPLE tion rate of million s.c.f.d. Fuel is injected thru line 32 to burner 30 at the rate of 42,000 s.c.f.d. This gas comprises a fuel gas recovered from the produced gases in line 36, after initiation of the process is effected with natural gas as the fuel. In this operation, a temperature of about 1200 F. is maintained adjacent the burner with a temperature at the uppermost level of the stratum of about 800 F. In this manner, the shale adjacent the production well is retorted so as to produce vaporized shale oil along with light gases which are recovered thru line 36. Continued retorting results in moving a heat zone thru the oil shale to the injection well.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

I claim:

1. A processfor producing oil from an oil-yielding stratum pentrated by an injection well and a production well, the permeability of said stratum being too low to permit forcing gases therethru, which comprises the steps of:

(a) providing a flow path for air between said wells at a level subjacent the bottom of said stratum;

(b) injecting air thru said injection well and producing it in said production well thru said flow path;

(c) admixing fuel with said air to form a combustible mixture in said production well;

(d) burning the resulting combustible mixture of step (c) in said production well Within said stratum so as to heat and produce oil therefrom; and

(e) recovering the oil resulting from the foregoing steps.

2. The process of claim 1 wherein a burner is positioned in said production well adjacent the bottom of said stratum and fuel is injected thru said burner to form the admixture of step (c).

3. The process of claim 1 wherein fuel gas is injected in admixture with the air of step (b).

4. The process of claim 1 wherein air is injected thru a central injection well surrounded by a ring of production wells and combustion is effected in each of said production wells.

5. The process of claim 1 wherein said stratum is an oil shale.

6. The process of claim 1 wherein said stratum is an oil shale, said passageway of step (a) is a fracture in the substratum held open with a propping material.

7. The process of claim 6 wherein fuel is injected thru a burner in said production well adjacent the level of the bottom of said stratum.

8. The process of claim 6 wherein said fuel is injected thru said fracture from said injection well.

0. The process of claim 1 wherein steps (b) thru (e) are continued, using a tubing string for injecting air thru said injection well, so as to heat said stratum from said production well to said injection well and produce oil in vapor form thru said injection well, thereby preheating the injected air.

10. The process of claim 1 wherein an inert diluent gas is injected with the air of step (b).

References Cited UNITED STATES PATENTS 2,584,605 2/1952 Merriam et a1. 166-11 3,147,804 9/1964 Wyllie 166l1 3,159,216 12/1964 Reed et al. l6611 3,250,327 5/1966 Crider 16611 3,342,258 9/1967 Prats 166-11 STEPHEN I. NOVOSAD, Primary Examiner US. Cl. X.R. 166-272 

